1. Field of the Invention
This invention relates to seismic exploration and particularly to a method and apparatus for determining the instant an explosive is detonated.
2. Description of the Related Art
In seismic exploration using explosives as the seismic source, it is desirable to know precisely, the instant of detonation. Currently, the time of detonation, commonly referred to as the "time break" is determined by measuring the time the electrical continuity between the two wire leads of a blasting cap is broken. Closing the switch in the detonator circuit causes a signal to be sent to the controller resulting from the brief flow of current through the circuit before the lead wires in the blasting cap are broken. Plasma generated by the explosion of the blasting cap conducts current in the circuit after detonation, thus the signal sent by the detonator to the time recorder is actually longer than that actually representing the instant of detonation. The accuracy of that method is in the order of 0.1 millisecond (ms). With the advent of more modern and accurate geophysical equipment, it is desired to determine the instant of detonation with an accuracy of one microsecond or better.